1. Field of the Invention
The present invention relates generally to drag reducing compositions comprising at least two different drag reducing polymers. More specifically, the present invention relates to drag reducing compositions comprising at least one drag reducing polymer formed by emulsion polymerization and at least one drag reducing polymer formed by bulk polymerization.
2. Description of the Prior Art
When fluids are transported by a pipeline, a drop in fluid pressure typically occurs due to friction between the wall of the pipeline and the fluid. Due to this pressure drop, for a given pipeline, fluid must be transported with sufficient pressure to achieve a desired throughput. When higher flow rates are desired through the pipeline, more pressure must be applied due to the fact that as flow rates are increased the difference in pressure caused by the pressure drop also increases. However, design limitations on pipelines limit the amount of pressure that can be employed. The problems associated with pressure drop are most acute when fluids are transported over long distances. Such pressure drops can result in inefficiencies that increase equipment and operation costs.
To alleviate the problems associated with pressure drop, many in the industry utilize drag reducing additives in the flowing fluid. When the flow of fluid in a pipeline is turbulent, high molecular weight polymeric drag reducers can be employed to enhance the flow. A drag reducer is a composition capable of substantially reducing friction loss associated with the turbulent flow of fluid through a pipeline. The role of these additives is to suppress the growth of turbulent eddies, which results in higher flow rate at a constant pumping pressure. Ultra-high molecular weight polymers are known to function well as drag reducers, particularly in hydrocarbon liquids. In general, drag reduction depends in part upon the molecular weight of the polymer additive and its ability to dissolve in the hydrocarbon under turbulent flow. Effective drag reducing polymers typically have molecular weights in excess of five million.
Some conventional drag reducers are employed in the form of polymer particles suspended in a continuous phase. Most typical drag reducers in this form can only contain up to about 23 weight percent of the drag reducing polymer based on the total weight of the drag reducing composition. Additionally, the efficacy of many drag reducers can be very inconsistent over the distance the flowing fluid travels. Accordingly, there is a need for improved drag reducers containing a higher weight percent of the active ingredient drag reducing polymers and having improved consistency of performance over the length of a pipeline.